Everybody seems to be doing zombies. I mean, there's a Jane Austen zombie thing out there somewhere.

BBC are probably a bit fussier about crossovers than Paramount are... back when Marvel had the Star Trek licence there was a Star Trek / X-Men crossover comic (which wasn't actually that bad, all things considered, but then I'll forgive a lot when the comic includes some classic confusion between two very... different... Dr. McCoys...)